Steel Wire Rod Cementite Aspect Ratio Control
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Solution Overview
Problem
Existing methods for improving the workability of steel wire rods, such as spheroidizing annealing, often result in uneven surfaces and increased costs due to excessive chromium addition, and fail to address the issue of microvoid formation during processing, leading to wire breakage and cracking.
Innovation Solution
A steel wire rod with a microstructural morphology of cementite, characterized by an aspect ratio of 2 or less, and specific chemical composition ranges, including C, Si, Mn, P, and S, to delay the formation of internal microvoids, enhancing wire drawability and forgeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If spheroidizing annealing is performed with large austenite grain size (100 μm or more) to improve forgeability, then workability is improved, but surface unevenness occurs on free surfaces during forging operations
Solution Approach 1:
The patent changes the microstructural parameters by controlling cementite aspect ratio (≤2) and abundance ratio (≥80%), rather than relying on large austenite grain size. This alternative parameter control achieves workability improvement without the harmful surface unevenness effect.
Solution Approach 2:
The patent applies local quality by controlling the morphology and distribution of cementite particles specifically, making them equiaxed with aspect ratio ≤2. This localized microstructural control improves workability at the particle level without affecting the overall grain structure and surface quality.
2Ease of operation
If Cr is added to promote spheroidizing of cementite after annealing, then workability is improved, but alloy cost increases and other problems are incurred
Solution Approach 1:
The patent replaces expensive Cr alloying with a cost-effective microstructural control approach. By controlling cementite morphology through processing parameters rather than expensive alloying, the invention achieves similar workability improvement without the high material cost.
Solution Approach 2:
The patent changes from chemical composition control (Cr addition) to microstructural parameter control (cementite aspect ratio and abundance ratio). This parameter transformation achieves the same functional effect with lower material cost.
3Productivity
If conventional heat treatment methods are used, then production efficiency is maintained, but microvoid formation occurs during working operations leading to wire breakage
Solution Approach 1:
The patent applies preliminary action by controlling the cementite microstructure before wire drawing operations. By pre-establishing the equiaxed cementite morphology with aspect ratio ≤2 and abundance ratio ≥80%, the material is prepared in advance to resist microvoid formation during subsequent working operations.
Solution Approach 2:
The patent applies preliminary anti-action by creating a microstructure that pre-resists the harmful effect of microvoid formation. The controlled cementite morphology acts in advance to prevent the initiation and propagation of microvoids during wire drawing and forging operations.
Data Source
Figure 1~2
Figure 3
Figure 4(A)~4(B)
AI summary
The present invention provides a steel wire rod with stable workability. The steel wire rod has steel components containing, by mass%, C: 0.20 to 0.60%, Si: 0.15 to 0.30%, Mn: 0.25 to 0.60%, P: ≤0.020%, S: ≤0.010%, and a balance of Fe and unavoidable impurities, and an internal microstructure including cementite, in which by number ratio, 80% or more of the cementite in a cross-section vertical to a longitudinal direction of the wire rod has a short axis of 0.1 µm or less and a ratio of a long axis to the short axis, defined as an aspect ratio, of 2.0 or less.